If you have the Gibbed Save Editor for Mass Effect 3, know that you can put multiple Weapon mods - and multiple copies of the same weapon mod for an additive effect - for a weapon that either Shepard or a Squad member carries around.->Open the Gibbed ME3 Save Editor->Open your save for your character->Switch to the Raw tab->Under the Section 3. Squad Player, is your weapon Mods section (you click on the [...] to open up the new window)->You can either add a weapon and put in the weapon class name section the desired weapon, like SFXGameContent.SFXWeapon_SniperRifle_JavelinOr SFXGameContentDLC_EXP_Pack003.SFXWeapon_AssaultRifle_Lancer->Then open up the [...] next to the weapon mod class names and add something like (if sniper):SFXGameContentDLC_Shared.SFXWeaponMod_SniperRifleSuperScopeSFXGameContent.SFXWeaponMod_SniperRifleDamageSFXGameContent.SFXWeaponMod_SniperRifleReloadSpeedSFXGameContent.SFXWeaponMod_SniperRifleTimeDilationSFXGameContent.SFXWeaponMod_SniperRifleConstraintDamageSFXGameContentDLC_EXP_Pack003.SFXWeaponMod_SniperRifleUltraLightSFXGameContent.SFXWeaponMod_SniperRifleReloadSpeedSFXGameContent.SFXWeaponMod_SniperRifleConstraintDamageSFXGameContentDLC_EXP_Pack003.SFXWeaponMod_SniperRifleUltraLightSFXGameContent.SFXWeaponMod_SniperRifleReloadSpeedSFXGameContent.SFXWeaponMod_SniperRifleConstraintDamageSFXGameContentDLC_EXP_Pack003.SFXWeaponMod_SniperRifleUltraLight

For Henchmen The process is pretty much the same.

NOTE: Some weapon mods I found to have an opposite effect, like the SFXGameContent.SFXWeaponMod_ShotgunAccuracy Actually makes the shotgun less accurate if you copy multiple lines of it into the desired weapon.Also, I have modded with a coalesced editor my weapon mods, so perhaps adding multiple lines of the same weapon mod might not have the same effect as I had, but do try and test this for yourself, say you save outside the spectre requisitions office and edit that save, then when you try it ingame, you have a good place to test out your weapons, the shooting range.NOTE2: If you even go to the "MODIFY" window ingame on a weapon bench/the squad loadout window when entering a new mission, your weapon mods will be reset from those specified in the save editor, because it doesn't normally allow more than 2 mods on a single gun.NOTE3: Because of the above limitation, I find that the first moment you find yourself ingame with a squad and infront of a weapon bench, I tend to just add to all weapons for all members some weapon mod (doesn't matter what) only because I feel lazy about copying in the save editor multiple new guns. So that when I open up the save editor, I can see for Shepard and my Henchmen the weapons available and what weapons they have modded, and I can just add into it (I have a text file with all weapon mods copied so I can simply copy-paste the needed names).You can still perfectly freely switch your weapons, and the mods stick on the weapons for all squad members as long as you don't go into the ingame weapon mod window to switch them around.So once you've added weapon mods to a gun or multiple guns, you can switch when you feel like it the gun around, and still have the mods in place.